1. Field of the Invention
The field relates to an organic light emitting display, and more particularly, to a method for driving a demultiplexer (demux) wherein when an RGB data signal is applied by using the demux, the RGB data can be stored in each storage capacitor of pixel circuits by applying the RGB data signal during a period in which an emission control signal is on regardless of a scan signal being on or off.
In addition, the field relates to a pixel circuit of an organic light emitting display. The pixel circuit uses fewer transistors so that the pixel circuit can be highly integrated. Consequently, high resolution can be accomplished. Furthermore, the threshold voltage of a driving transistor can be compensated for, and IR-drop of a first power supply line can be improved.
In addition, the field relates to a method for driving a demultiplexer (demux) including white balance compensation.
2. Description of the Related Technology
Recently, organic light emitting displays have been used as a flat panel display because they are thin, have a wide viewing angle and have high speed responsiveness.
The organic light emitting display can control the brightness of each pixel and display an image by controlling the amount of electric current flowing through an organic light emitting diode(OLED).
That is to say, once a current corresponding to a data voltage is supplied to an organic light emitting diode, the organic light emitting diode emits light corresponding to the current supplied. Here, the data voltage applied to the organic light emitting diode has a value of various steps within a predetermined range in order to display a grey scale.
When a thin film transistor, which adopts amorphous silicon (a-si), is used, it has a weakness in that ability for driving a current can be relatively low. However, it also has merits in that the uniformity of the display device is excellent, and it is more suitable for being manufactured in a large-sized display.
In addition, in case that RGB data signals are applied to pixel circuits by using a demux, if the emission control signals applied through the emission control line (EM[N]) coupled to the pixel circuits are turned off, the RGB data signals can be stored in a storage capacitor of the pixel circuit improperly.
That is to say, in case that RGB data signals (voltages) are applied by driving a demux continuously on the condition that the RGB data signals (voltages) which are already stored in the storage capacitors are not yet initialized, it can cause a problem in that proper RGB data signals (voltages) cannot be stored in the storage capacitors.
The uniformity of the luminance of the display panel can have low quality because a driving transistor of the respective pixel circuits of an organic light emitting display can have different threshold voltages. In addition, the lower portion of the panel can have even worse luminance because IR-drop occurs as a first power supply line (VDD) passes through the respective pixel circuits.
In case that a pixel circuit of an organic light emitting display includes a large number of transistors, it can impede high resolution of the panel equipped with the pixel circuit because high integration becomes impossible.
In the case of conventional circuits for compensating the threshold voltage of a driving transistor in the pixel circuit, a path from a control electrode of the driving transistor to a negative power supply voltage is formed, and then a leakage current can flow through the path. Consequently, it can cause an improper emission of an organic light emitting diode.
In the case of a full color organic light emitting display, a full color display can be accomplished by equipping the display device with an organic light emitting diode which emits light of three colors of red, green and blue. However, the materials used as an organic light emission layer can be degraded by the heat generated during self emission. Because of the degradation, the luminance of the organic light emitting diode can deteriorate. As a result, the life span of the organic light emitting diode can be limited.
Because the degree of the degradation of an organic light emission layer which forms a red, green and blue organic light emission layer differs from one another, the difference of the luminance of the red, green and blue organic light emission layer can become larger as time goes by. Accordingly, the desired color cannot be reproduced because of the different rates of degradation of the red, green, and blue layers. That is to say, because each emission layer corresponding to red, green and blue has a different life span from one another, the white balance is difficult to maintain in case that the emission layer is driven for a long time.